User interfaces that are used to translate human movements to machine movements are used in myriad industries. For example, some aircraft flight control systems include a user interface in the form of one or more control sticks, pedals, or other mechanisms. The flight control system, in response to input forces supplied to the user interface(s) from the pilot and/or co-pilot, controls the movements of various aircraft flight control surfaces. No matter the particular end-use system, the user interface preferably includes some type of mechanism to supply haptic feedback, through the user interface, to the user.
Many haptic feedback mechanisms are implemented using a force sensor as the primary input device to the feedback loop. In most instances, the force sensor drives some type of servo amplifier, which in turn drives a motor. The motor, which may be coupled to the user interface via a gearbox, supplies a feedback force to the user interface. Although these types of haptic feedback mechanisms are generally safe and reliable, they do suffer certain drawbacks. For example, the force sensor (or sensors) that are typically used are relatively high-fidelity force sensors, which increase overall system cost and complexity. Moreover, when redundancy and minimization of cross-axis coupling are employed to increase overall system reliability, the increased cost and complexity can be significant.
Hence, there is a need for a method of sensing the force in a user interface system that exhibits suitable fidelity, redundancy, and/or minimal cross-axis coupling, without significantly impacting overall system cost and complexity. The present invention addresses at least this need.